This invention relates generally to the field of relatively small motion transmitting clutches which serve to lock a motion output member against movement in the absence of input motion imparted by a user, and which will assume a disengaged mode for the transmission of such input motion. Devices of this general type are known in the art, and the invention lies in specific constructional details which provide improved operation, facilitated manufacture, and extended useful life. While not limited to application in any particular area of utility, the disclosed embodiment is particularly useful as a component of shade or blind hardware installed in a window.
Venetian blinds and similar shades include an upper horizontal member carried by a fixed valance. The slats are carried by vertical tapes having horizontal support members which may be angled to rotate the slats. The entire blind is raised or lowered by a vertical cord entrained upon a horizontally mounted rotatable shaft and connected to the lowermost slat. The blinds are relatively heavy, and the shaft is, accordingly, provided with a motion inhibiting clutch for maintaining a desired adjustment against the weight of the unwound segment of the blind. To a lesser extent, the same action occurs when using a flexible planar shade.
It is known in the art to employ for this purpose clutches employing a spirally wound radially contractile spring, or plurality of springs, which expand to allow movement of an enclosed shaft, and contract to grip the shaft against further rotation when imparted motion transmitted through a pulley ceases. While not without utility, clutches of this type have several serious shortcomings, most of which are sourced in the problem of releasing the shaft for movement by initially imparting a spring expanding force at one end of the spring. Clutches of this type do not lend themselves to manufacture in the form of injection-molded parts, and are otherwise relatively expensive to manufacture because of less than simple assembly.